Sony Trinitron KV32FV27 Power Supply Problem

[cmonkey]

I'm just creating this thread to document this issue so I don't forget what I've tested so far.

Technical Manual.

I've measure CN641 on the power supply board ( board G ) and all the voltages are about half of what they should be. So the 9V pins are measuring about 5V, the 135V pins are measuring about 70V.

I replaced the two large main caps ( C606 and C607 ) and also C643 and C641 with new capacitors without doing any more troubleshooting and strangely the TV worked for about 30 minutes and then started behaving the same way.

I can't figure out if it's an AC or a DC side issue ( I don't know how to test the transformers and don't know their output values), so I just started measuring the voltage points in the schematic that have values. I started with IC601 since that is on the AC side and I can get 120V all the way up to it but then it gets weird. Maybe my multimeter can't measure the voltages coming off it?

I also tested the transistor's diodes (still in circuit) and got some strange results. On the bottom of the board the pins are labeled B1, C1, E1 and B2, C2 and E2 so these must be each diodes base, collector and emitter.

I get voltage drops as follows -

B1 -> C1 = 0.459
B1 -> E1 = 0..529

B2 -> C2 = 0.459
B2 -> E2 = 0.529

Those are as expected, but then I measure across the two diodes and also got a voltage drop.

B2 -> C1 = .0529

I'm not sure if this is normal or not. I also get continuity between E2 and C1 so there is a low enough resistance between them to register as a short.

C1, E2 and B2 are also the pins I get weird voltage readings on as well. Maybe I need to test it out of circuit?

Here is a photo of the schematic.

[cmonkey]

Preface for today - this TV is acting very strangely, whatever fault it has on the power supply isn't constant. About 1 in 10 times I turn this thing on, it's got good voltage coming off the power board and everything works for a few minutes. Then the voltage starts slowly dropping and the picture starts warping until I turn it off. Then it's back at about half the right voltage.

I'm just creating this thread to document this issue so I don't forget what I've tested so far.

Technical Manual.

I've measure CN641 on the power supply board ( board G ) and all the voltages are about half of what they should be. So the 9V pins are measuring about 5V, the 135V pins are measuring about 70V.

So this isn't entirely accurate. The 5V standby voltage is good (pin 10 on CN641) and the power on voltage (pin 11) is also good at about 3.6V.

I also think the short between E2 and C1 might be ok because they are connected via FB604 which is a ferrite bead and all the other FB components are also measuring the same. I would need to remove IC601 from circuit to properly test it I think.

I've also tested the 3 bridge rectifiers in circuit with just a diode test and they are all measuring good. (D602, D641 and D643)


So for now I have ordered a proper good LCR meter so I can test all the capacitors. My DMM isn't working on capacitance anymore.


Until then I need to figure out how to properly test voltages on the HOT side of this board. I realized I wasn't measuring the pins coming off IC601 properly because I thought it was AC current but it looks like these are DC because they are after the bridge rectifier. Am I wrong here?

What do I use for a ground when testing DC on the hot side of a power supply? Specifically I'm trying to test the pins on IC601 to see if the voltages are the same as in the schematic.

[Donny2derby]

Diodes don't have bases, collectors and emitters. They have Annodes and Cathodes. Transistors have Base, collector and emitter terminals.

If you want some proper help it's best you post up some pictures of all the boards.

[Diah]

in General over all HOT area on PSU the - GND will be references to the main filter CAP -, Cold area will be TV chassis

[cmonkey]

Diodes don't have bases, collectors and emitters. They have Annodes and Cathodes. Transistors have Base, collector and emitter terminals.

If you want some proper help it's best you post up some pictures of all the boards.

So the transistor is tested in diode mode, but doesn't have internal diodes? I'll try to post a photo later.

[Donny2derby]

So the transistor is tested in diode mode, but doesn't have internal diodes? I'll try to post a photo later.

A transistor acts as a switch, a diode is there to allow current to only pass in one direction.

A transistor is 3 terminal, diode has 2.

There is a diode in a transistor so that's why they can be tested in Diode mode using a multimeter.

[cmonkey]

A transistor acts as a switch, a diode is there to allow current to only pass in one direction.

A transistor is 3 terminal, diode has 2.

There is a diode in a transistor so that's why they can be tested in Diode mode using a multimeter.

Ok that's kinda what I thought.

Here's a photo. The AC input is on the upper left. The transistor I'm looking to test voltages on is bottom right. The main bridge rectifier is middle leftish.

Am I wrong is noticing that it looks like the AC is the striped section and DC is non-striped?

[Donny2derby]

I'm not experienced enough to be able to distinguish if it's only AC on the striped and DC non striped but you will only have AC before the bridge rectifier and DC after that.